It is previously known that a septic system of a building such as a residential home contains residual heat which has the potential to be extracted and used to heat the building.
The septic system collects liquid waste material from the building and stores this within a tank where anaerobic bacterial activity acts upon the waste material to break down solids. The anaerobic bacterial activity generates heat and also heat is added to the system from warm water used within the building.
Previous attempts to extract heat from the septic system have generally used heat pumps where a pipe circulates water under the ground into the septic system in a closed loop where an inner end of the pipe acts as an input into a heat pump which transfers heat from the circulating water to a heated side of the heat pump to transfer that heat into a furnace of the building.
Such heat pump systems are not generally popular and have not achieved widespread acceptance partly due to the complexity and partly due to inefficiencies in the system which do not provide the expected economies.
One example is shown in U.S. Pat. No. 3,986,344 (Newman) issued Oct. 19, 1976 where the circulating water is passed through a pipe which is wrapped around the outside of the tank and within the area of the septic system where the waste liquid is discharged from the tank. This system has not achieved widespread acceptance.
Another factor which must be taken into account is that the septic system requires a certain temperature for the anaerobic activity to occur so that it is not possible to operate a system which extracts sufficient heat from the septic system to interfere with this bacterial activity.